Current limiting fuse



H. RAwLlNs ET AL 2,309,013A

CURRENT LIMITING FUSE Filed Sept. 19, 1940 Jan. 19, 1943.

terrupters, and

which are capable of automatically interrupting current limiting means,

inghouse Electric &

East Pittsburgh, Pa.,

vania Application Graybill, Turtle Creek, Pa., assignors l Patented Jan. 19, l .n 2,309,015

UNITED sTATEs e. PATENT OFFICE CUBBENTZl'IING FUSE Herbert L. Rawlins, Wilkinsburg, and Howard W.

West- Manufacturing Company, a corporation of Pennsyl- Septeniber 19, k19M, Serial No. 351,394

11 claims. (ci 20o-izo) This invention relates generally to circuit inmore speclcally to interrupters a circuit in response to the passage therethrough of currents above a predetermined value, and at the ularly disclosed is capable of limiting blows.

This invention relates especially to a current limiting interrupter or fuse of the type where an arc establishing means such as a fusible means is provided in shunt relation with respect to a and is confined so th the arc formed upon operation of the arc establishing means has a high arc voltage so as to quickly transfer the current to the current limitingmeans. The current thus limited is easily interrupted by a circuit interrupting means which may be a second fusible means.

Current limiting means disclosed in' the copending .applications of H. L. Rawlins, Serial No. 357,393, filed September 19, 1940, and A. P. Strom, Serial No. 357,395, filed September 19, 1940, and both assigned to the same assignee of this invention.V The instant invention relates to certain improved construcand ons the current when the fuse A further object of this invention is to provide a novel means for supporting a fuse wire in a closely coniined arc passage having walls of an insulating material.

Another object of this invention is to provide a novel means for sealing a fuse wire in a closely restricted fuse passage.

Another object of this invention is to provide a novel arrangement and construction o! a current limiting fuse of the type described which is particularly emcient in operation, relatively simple in design and economical to manufacture. objects of this invention will become more apparent upon consideration of the following detailed description of preferred embodiments thereof, taken in connection with the attached drawing in which:

Figure l is a substantially central section view of a current ing fuse ed in accordance with the`invention.

Fig. 2 is a transverse sectional view taken substantially on the line II-KII of Fig. l.

Fig. 3 is a central, longitudinal sectional view of a modiiied form of fuse constructed in accordance with this invention.

longitudinal constructan inner porin Figs. l and 4 is an elevational view of tion of the fuse shown of this general type are Fig. 5 is an enlarged fragmentary sectional view of threadedly engaging portions of the fuse shown in Fig. l, and

Fig. 6 is a partial elevational view of the lower end of the fuse shown in Fig. 3, with the indicator shown in an indicating position.

Referring first to the embodiment of the invention shown in Fig. l, the fuse there illustrated comprises an outer insulating fuse tube 2 which may be of any desired insulating material, such, for example, as liber or a synthetic resin, or a like material which has the property of being capable of evolving an arc extinguishing gas arc. The fuse I these caps may be in any desired manner, such, for example, as by depressing a portion 5, 1 of the cap ilanges inwardly into the material of the fuse tube I.

Referring to Fig. 4 of the drawing, there is illustrated an inner insulating tubular'sleeve l having a threaded exterior surface designed to be threadedly engaged with the threads provided on the interior wall at-the upper end of fuse tube 2. It will be noted that the threads both on inner tube l and outer fuse tube 2. are multiple threads, and, as shown in the drawing. are eight-lead threads. Before the inner insulating fuse tube 2, howat least one of 4. The fuse having a high temperature melting point, such, for example, as silver, and although the fuse wire Il is shown as being laid in only one thread of the multiple threads of inner tube 8, obviously for fuses of higher capacity, parallel fuse wires may be laid in one or more intermediate threads of inner tube l. After the fuse wire Il is wound in a thread of inner tube l, the wire and tube are then coated with a viscous paint I2 (Fig. 5) constituting is capable of evolving an arc extinguishing gas when in proximity to an electric arc and a solvent therefor, such, for example, as,cellulose acetate or ethyl cellulose solution. The inner and coating ins i2 seals I on inner tube 8, and also coating l2 seals the thread in which fuse wire l0 is laid, from adjacent is clearlyl indiwire i melts, but also insulates adjacent turns 10 the current will be very quickly transferred to struction of fuse tube 2 and inner tube 8. 15 chamber. When a resistor having valve charblock preferably of a non-metal1ic resistance The manner in which fuse wlre l0 is mounted material such as carbon or carborundum. Such is of importance because this mounting, while a resistor should preferably be in the form of being relatively simple to assemble, is extremely iinely divided resistance particles bonded toeective in providing a high resistance path for current limiting resistors disclosed in said coshould occur in a small fraction of a half cycle pending application of A P Strom The block before the short circuit current has had a chance i4 is preferably secured in inner tube 8 by ceto build up to any dangerously high value. With inenting the same in position, and a coil comthe construction illustrated, the current may be pression spring of conducting material I6 is pro- 30 transferred from the spiral path between fuse vided between the upper end of the resistor block tube 2 and inner tube 8 in approximately onei4 and end cap 4, to conduct current from the tenth of a cycle depending, of course, upon the end cap to the upper end of the resistor block. available current. Such speed in transfer is also through an aperture 20 in an insulating closure 40 sioning fuse wire I8 is positioned in such a manduced extension 2l which engages terminal cap many of the parts of the fuse shown in these 6 to maintain the closure disk 22 in operative iigures are identical with those already described position against shoulder 2| formed on the fuse 50 in connection with the embodiment of the intube. The extension 24 serves to support an vention shown in Figs. i. 2 4 and 5, like referenlongated coil tension spring 26 which has one ence numerals are used to designate such like end thereof angularly extended through an apparts, and to .avoid repetition these parts will not erture in disk 22 to be bent over as at 29, on the be again describedin detail. The'current limiting opposite side of the disk to thereby anchor this means in this embodiment oi' the invention comend of the spring to the disk. The other end prises a pair of blocks 3l oi' resistance material of the coil spring is pulled out or tensioned, and similar to the material constituting the resistor end cap 6 to be secured therein as at 30, by sol- 60 mounted therein. The i'use shown in Figs 3 capable of evolving an arc extinguishing gas the hating effect thereof. A conducting metal example, as boric acid, gypsum or the like. lower end of inner tube 8 as Wn in Fi 3. In the operation of the fuse shown in Figs 1, and this partition disk is provided with a sub- 2, 4 and 5, uponlthe occurrence of a short cirstantially central aperture 38 for receiving the cuit, fuse wire I8 melts ilrst, since it has a lower 70 lower end of fuse wire I0 and the upper end of melting point than fuse wire I0. However, fuse fuse wire I8 to be secured therein, for example, wire i0 also melts substantially immediately as by soldering or the like. A coil compression thereafter because although it has a higher spring I is provided between partition disk 38 melting point than fuse wire I8, its melting point and lower resistor block 3l which, in cooperation is much below that of normal short circuit with spring IB, maintains a amounts of current partition disk 36. Instead of utilizing powdered arc extinguishing material, such as the material 32 described in connection with the embodiment of the invention shown in Fig. 1, it is preferred to use blocks 42 which may be of the same material as the material 32 previously referred to, but compressed or otherwise formed fln'to blocks with a passage 43 extending substantially centrally through each block to receive fuse wire I8. It will be noted that in this embodiment of the invention fuse wire I8 extends downwardlyy through an aperture 44 in end cap 6 and through an aperture in an indicating disk 46, to be bent over and secured to the disk as at 45, by solder or the like. A

A spiral compression coil spring 48 is provided betweenv indicating disk 46and-end cap 6, with the outer coil 50 of the spring secured to indicating disk 46, for example, as by soldering or the like; and the inner coil 52 of the spring is secured to end cap 6 in a like manner. Asv shown in Fig. 3, normally fuse wire I8 maintains spring 48 in a compressed conditionso that the indicating disk 46 lies closely adjacent the end cap 6.

The operation of this embodiment of the invention is substantially identical with that of the embodiment of the invention illustrated in Figs. 1, 2, 4 and 5, of the drawing, and therefore it will not be again specified in detail to avoid repetition. On short circuits, both fuse wires I8 and I will blow as before, the current will be shifted-to resistor blocks 34, and finally interrupted in bores 43 through blocks 42. Obviously as soon as fuse wire I8 melts, coil spring 48 will not only act to withdraw any lower unfused portion thereof, but will also act to move indicating disk 46 to a projecting position with respect to the terminal cap 6 to thereby provide a readily visible indication that the fuse-has blown. This position of the indicating disk 46 is shown in Fig. 6 of the drawing.

As previously stated, fuse lower currents than fuse wire I0, with fuse wire I8 preferably being of a size to interrupt currents according to the rating of the fuse and may, for example, be fusible on currents of 1 or 2 lamperes, whereas fuse wire I0 need not blow until the current exceeds a value above which it is desirable to limit the current in order to prevent damage to circuits and apparatus served thereby, and therefore fuse wire I0 may. for exv,.fample, not fuse until currents reach a relatively high value such, for example,` as 80 amperes. From this illustration, it is obvious that when fuse wire I8 blows on relatively small' currents, that is, in the illustration given, currents less than 80 amperes, fuse wire I0 need not blow at all inasmuch as these currents can be easily interrupted by fuse wirel due to elongation of the are formed by coil spring 26 of ment shown in Fig. l, and spring 48 in the embodiment shown in Fig. 3, along the arc ex-,

tinguishing material 32 or 42,` to thereby increase the arc voltage by elongation of the arc, and evolution of arc extinguishing lgas in the path of the arc will extinguish the arc. vSuch a method of extinguishing an arc, if limited to low current arcs, can be carried out by means assembled in a relatively small space, and, accordingly, the structures illustrated, since they will never be called upon tol interrupt large due to the efilcient current limiting action thereof, can be made of relatively simple and compact construction as illustrated.

, the shunt path to wire I8 melts on In the foregoing there has been disclosed modifications of a novel type of current limiting fuse having no vel means for mounting a shunt fuse for a current limiting resistor means, to obtain exceptionally quick transfer of the current from the resistor. A novel arrangement of parts in a fuse including a resistor and shunt and series fuses has also been disclosed, together with novel biasing means for the se- 'ries fuse which may also include an indicating means for indicating the condition of the fuse.

Having particularly described preferred embodiments of the invention as provided in the patent statutes, it should be understood that the invention is not to be limited to the specific embodiments herein disclosed, inasmuch as it will be obvious, particularly to persons skilled in the art, that many changes and modifications may be made in these particular constructions without departing from the b road spirit and scope of this invention. Accordingly it is desired that the invention be interpreted as broadly as possible and that it be limited only by the prior art and by what is expressly stated in the following claims.

We claim as our invention:

1. In a circuit interrupter, a pair of telescoping loosely threadedly engageable members of insulating material with the thread on each ci said members comprising a multiple thread so as to provide a plurality of separate, restricted spiral arc passages at the bases of the threads on at least one of said members, and means for striking an arc in one of said arc passages, whereby the intermediate threads provide a tortuous path between successive turns of said one passage.

2. In a circuit interrupter, a pair of telescoping loosely threadedly engageable members of insulating material with the thread on each member substantially entirely filling the thread groove on the other member so as to form a restricted spiral arc passage at the base of a thread on at least one of said members, a fusible wire positioned in said passage, and means of insulating material for sealing said wire in said passage and for sealing oil adjacent turns of said passage to further restrict said arc passage and to prevent ilashover between the turns thereof.

3. In a circuit interrupter,. means of insulating material having a surface provided with a plurality of spaced, substantially ,parallel continuous grooves therein to form arc passages, a second means of insulating material having a surface contiguous with respect to said grooved surface, and having a plurality of correspondingly spaced and parallel continuous projections adapted to substantially ll said grooves to restrict said arc passages with said members maintained in substantially fixed relation, and means for striking an arc in certain of said passages, with at least one other passage between said certain passages to provide a tortuous path therebetween.

4. In a circuit interrupter, a pair of telescoping loosely threadedly engageable members of insulating material adapted to form a restricted spiral arc passage at the base of a thread on atleast one of said members, a fusible wire positioned in said passage, and means of insulating material whichis capable of evolving an arc extinguishing gas when in proximity to an electric arc for sealing said wire in said passage and for sealing olf adjacent turns of said passage to further restrict said arc passage and to prevent flashover between the turns thereof.

5. In a circuit interrupter, means of insulating material having a surface provided with a continuous groove therein to form an arc passage, a seoond means of insulating material having a surface contiguous with respect to said grooved surface, and having a continuous projection adapted to substantially illl said groove to restrict said arc passage with said members maln- 4'fined in substantially fixed relation, means for striking an arc in said passage, and means of a material capable of evolving an arc extinguishins gas when in proximity to an electric arc for sealing said e.

6. In a circuit interrupter, a pair of loosely threadedly engaged, telescoping tubes of insulation material, adapted to form a restricted spiral arc passage at the base of a thread on at least one of said members, means for striking an arc in said arc passage. and current limiting means located in the inner one of said tubes and connected in parallel relation with said means for striking an arc.

'1. In a fuse, a fuse tube having terminals adjacent opposite ends thereof, an inner tube telescopically engaging at least a portion of the inner wall of said fuse tube. at least one of said tubes having a shallow spiral groove on the surface confronting the other tube to form a restricted spiral arc passage, current limiting means in said inner tube, a fuse wire positioned in said passage, -and shunting said current limiting means, and means connecting said current limiting means and fuse wire between said terminals.

8.Inafuse, afusetubehaving terminals adjacent opposite ends thereof, an inner tube telescopically engaging at least a portion of the inner wall of said fuse tube, at least one of said tubes having a shallow spiral groove on the surface confronting the other tube to form a restricted spiral arc passage, current limiting means in said inner tube, a fuse wire 'positioned in said passage and shunting said current limiting means, and means connecting said current limiting means and fuse wire between said terminals including fusible means.

9. In a fuse, a fuse tube having end terminal closure means at opposite ends thereof, transverse terminal partition means in said tube iritermediate the ends thereof to form a pair of chambers, current limiting means in one of said chambers, resilient means for maintaining said current limiting means in engagement with at least one of said terminal means, shunt fusible means for said current limiting means, and series fuse means connecting said current limiting means to another of said terminal means.

10. In a fuse, a fuse tube having terminals adjacent opposite ends thereof, current limiting means and shunt fusible means therefor connected to one of said terminals, series fusible means connecting said current limiting means and shunt fusible means to the other of said terminals, and means biasing said series fusible means to separate the ends thereof when said series fusible means fuses.

1l. In a fuse, a fuse tube having terminals adjacent opposite ends thereof, current limiting means and shunt fusible means therefor connected to one of said terminals, series fusible means connecting said current limiting means and shunt fusible means to the other of said terminals, means biasing said series fusible means to separate the ends thereof when said series means located in the inner one o and for securing said members relation with said current fusible means fuses, and indicating means movable toa projecting position with respect to said fuse tube by said biasing means when the fuse blows.

l2. In a circuit interrupter, means of insulating material having a Vsurface provided with a continuous groove therein to form an arc passage, a second means of insulating material having a surface contiguous with respect to said grooved surface te cover said groove, a fuse wire in said groove, and means of an insulating ad hesive material in said groove for sealing said wire therein and securing said insulating means together.

13. In a circuit interrupter, a pair of telescoping loosely threadedly engageable members of insulating material adapted to form a restricted spiraiarcpassageatthebaseofathreadon at least one of said members, a fusible wire positioned in said pasage, and means of an insulating adhesive material for sealing said wire in said passage, sealing oil' adjacent turns of said passage to further restrict said are passage and to prevent ashover between the turns thereof.

together.

14. In a circuit interrupter, a pair of telescoping tubes of insulation material, at least one of said tubes having a shallow spiral groove on the surface confronting the other tube to form a restricted spiral arc passage, means for striking an arc in said arc passage, and current limiting of said tubes and connected in parallel relation with said means for striking an arc.

15. In a fuse. a fuse tube having end terminal closure means at opposite ends thereof, transverse terminal partition means in said tube intermediate the ends thereof to form a pair of chambers, current limiting means in one of said chambers, resilient means for maintaining said current limiting means in engagement with at least one of said terminal means, shunt fusible means for said current limiting means, and series fuse means in the other of said chambers connecting said current limiting means to another of said terminal means.

16. In a fuse, a fuse tube having terminals adjacent opposite ends thereof, an inner tube telesoopically engaaing at least a portion of the inner wall of said fuse tube, at least said inner tube having a shallow substantially spiral groove on the periphery thereof to form with said fuse tube a restricted substantially spiral arc passage. current limiting means in said inner tube. a fuse wire positioned in said passage in shunt limiting means, and means connecting said current limiting means and fuse wire between said terminals.

17. In a fuse, a fuse tube having terminals adjacent opposite ends thereof, current limiting means and shunt fusible means therefor connected to one of said terminals, series fusible means connecting said current limiting means and shunt fusible means to the other of said terminals, said shunt fusible means having a higher melting point than said series fusible means, and means biasing said series fusible means to separate the ends thereof when said series fusible means fuses.

T L. RAW'LINB. HOWARD W. GRAYBILL. 

